Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$144.41	6.709%	$154.0985	$154.10	$154.10	$154.10
Purchase #2	$117.52	3.110%	$121.1749	$121.17	$121.15	$121.20
Purchase #3	$190.28	13.674%	$216.2989	$216.30	$216.30	$216.30
Purchase #4	$151.95	12.641%	$171.158	$171.16	$171.15	$171.20
Purchase #5	$69.62	11.672%	$77.746	$77.75	$77.75	$77.70
Purchase #6	$95.32	5.424%	$100.4902	$100.49	$100.50	$100.50
Purchase #7	$150.89	7.666%	$162.4572	$162.46	$162.45	$162.50
7 purchase totals =	$919.99		$1,003.4237	$1,003.43	$1,003.40	$1,003.50